Exhaust gas filters for Diesel engines have the purpose of filtering the soot out of the exhaust gas of the Diesel engines. The emission of soot from Diesel engines is undesirable because the surface of the soot particles contains small amounts of adsorbed substances, some of which, in high concentrations, are considered harmful to human health
The soot filters for Diesel engines conventionally consist of a monolith of porous ceramic material which consists of thin-walled ducts that are parallel to one another and are positioned along its whole length in the flow direction of the exhaust gas. These ducts are alternately closed at the upstream or the downstream end. The ducts are frequently alternately opened or closed in a checkerboard pattern so that each duct has an open and a closed end. Alternatively, in a manner similar to the production of corrugated cardboard, the filter may be wound in a spiral shape to form a gas-permeable packet In this case, the covering of the individual ducts is no longer only constructed in the manner of a chessboard but is also spiral-shaped.
When the Diesel emissions are led through this type of filter, the exhaust gas that enters through the ducts which are open on the inlet side is forced to flow laterally through the porous duct walls into the adjacent ducts which are open on the outlet side. In this case, the soot particles that can no longer pass through the duct walls accumulate in the ducts that are open upstream. When a certain ignition temperature is reached and when a sufficient oxygen concentration exists in the exhaust gas, the accumulated soot burns off and the filter is regenerated. Between two regeneration processes of this type, there is a considerable rise in exhaust gas counterpressure with increased loading of the filter. In the case of an especially high load, the burning-off of soot becomes very intense. Since a large part of the soot and the foreign substances accumulates in front of the closing means of the ceramic body on the outlet side, very high temperatures occur there which may become so high that the melting point of the ceramic material is exceeded and the filter is destroyed.
The objective of this invention consists of finding an exhaust gas filter for Diesel engines made of a porous ceramic material where the danger of a destruction of the filter through the burning-off of soot is largely avoided:
This objective is achieved by structuring a monolithic filter block made of a porous ceramic material having a plurality of ducts extending in the flow direction of the exhaust gases, wherein the ducts are alternately closed at the upstream or the downstream end, and wherein the closing means of the flow ducts at the downstream end in the flow direction, are staggered with respect to one another.
It was found by means of this staggering of the closing means of the flow ducts at the down stream end, a better distribution of the heat occuring during the burning-off of soot is possible. Due to the more even distribution of heat, damage to the filter material is largely avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.